1. Field of the Invention
The invention relates to dual fuel engines and, more particularly, relates to a system and method for coordinating operation of multiple dedicated controllers to control operation of gaseous fuel and liquid fuel supply systems of a dual fuel engine. The invention additionally relates to an engine incorporating such a control system.
2. Discussion of the Related Art
Recent years have seen an increased demand for the use of gaseous fuels as a primary fuel source in compression ignition engines. Gaseous fuels such as propane or natural gas are considered by many to be superior to diesel fuel and the like because gaseous fuels are generally less expensive, provide equal or greater power with equal or better mileage, and produce significantly lower emissions. This last benefit renders gaseous fuels particularly attractive because recently enacted and pending worldwide regulations may tend to prohibit the use of diesel fuel in many engines. The attractiveness of gaseous fuels is further enhanced by the fact that existing compression ignition engine designs can be readily adapted to bum gaseous fuels.
One drawback of gaseous fuels is that they exhibit significantly higher ignition temperatures than do diesel fuel, oil, and other liquid fuels traditionally used in compression ignition engines. In fact, the temperature of gaseous fuels does not increase sufficiently during operation of standard compression ignition engines for auto-ignition. This problem can be overcome by injecting limited mounts of pilot fuel, typically diesel fuel or lube oil, into the cylinders of the engine in the combustion chamber. The pilot fuel ignites upon injection and bums at a high enough temperature to ignite a gaseous fuel charge in the combustion chamber. Engines fueled in this manner are usually referred to as xe2x80x9cdual fuel engines.xe2x80x9d Some dual fuel engines are at least selectively additionally operable in either a xe2x80x9cdual fuel modexe2x80x9d as described earlier in this paragraph or in a xe2x80x9cdiesel only modexe2x80x9d in which the engine""s gaseous fuel supply system is disabled and the liquid fuel supply system is controlled to effect a standard diesel cycle.
At least one known dual fuel engine is operated by two dedicated controllers. The first, or dual fuel controller, is configured to control operation of the gaseous fuel supply system of the engine. The second, or diesel controller, is configured to control operation of the liquid fuel supply system of the engine. In the dual fuel mode, the dual fuel controller controls operation of the diesel controller in a master-slave relationship, with the diesel controller controlling liquid fuel supply timing and/or quantity as commanded by the dual fuel controller and the dual fuel controller controlling all other aspects of engine operation. In the diesel only mode, the gaseous fuel supply system is disabled and the traditional diesel cycle operation is maintained by the diesel controller.
The controllers of the system described above are coupled to one another by a hardwire link consisting of three lines. The diesel controller transmits desired engine speed to the dual fuel controller via one of these lines. The dual fuel controller responds by transmitting a diesel fuel injection quantity and timing command to the diesel controller over another of the lines. The hardwire interface is incapable of transmitting any information other than these specific, simple commands. As a result, all information required by both controllers for the performance of their functions must come from dedicated inputs. Each controller therefore requires a dedicated intake air temperature sensor, a dedicated intake air pressure sensor, and a dedicated input/output port for communicating with a manual interface such as a laptop computer. This need for redundancy considerably increases the complexity and expense of the control system. The duplicate sensors can also be difficult to physically incorporate into some engine designs. Similarly, some vehicle dashboards have less than ample room for multiple input/output ports. Moreover, the need to program both controllers individually requires substantial duplication of programming effort.
The hardwire interface employed by the control system described above also is susceptible to interference from external electrical signals. The resultant noise can hinder the transfer of information between the controllers, sometimes to the point that the system cannot differentiate signals of interest from noise.
The need therefore has arisen to increase the communication capabilities between the controllers of a dual fuel engine in order to simplify the structural and functional requirements of the system.
The need has additionally arisen to facilitate the programming of the controllers of a dual fuel engine.
The need also has arisen to facilitate the additional sub-system(s) such as EGR, water injection and/or other aftertreatment and pretreatment systems added on to the existing engine combustion control system.
In accordance with a first aspect of the invention, a dual fuel engine control system is provided with first and second dedicated controllers, each controlling some aspects of the operation of a dual fuel engine.
In accordance with a second aspect of the invention, the first and second controllers are linked together to allow them to share information for use in controlling operation of the engine.
An additional dedicated subsystem controller may also be provided with communication capability with the broadband communications link and operable to control another subsystem of the engine based at least in part on information transmitted to it over the broadband communications link.
In accordance with a third aspect of the invention, a method is provided for collecting data regarding engine operation, transmitting data from data collection sensors to the controllers, transmitting data between the controllers, and using the controllers to control the operation of the engine based on the engine operation data.
In accordance with a fourth aspect of the invention, the controllers are linked together with a broadband link.
Other aspects and advantages of the invention will become apparent to those skilled in the art from the following detailed description and the accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications could be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.